1. Field of the Invention
The present invention relates to a method of manufacturing a lithographic printing plate support, a lithographic printing plate support, and a PS plate. In particular, the present invention relates to a lithographic printing plate support which becomes the support of a PS plate having excellent printing performances and ability to withstand repeated printing, and to a manufacturing method which enables the lithographic printing plate support to be manufactured with high production stability, and to a PS plate having the above merits.
2. Description of the Related Art
Generally, a lithographic printing plate support is manufactured by the following processes being carried out successively. While an abrasive slurry, in which an abrasive is suspended in water, is supplied to the surface of an aluminum or aluminum alloy plate (hereinafter, xe2x80x9caluminum platexe2x80x9d) or a web or the like, the surface is subjected to a mechanical surface roughening treatment in which mechanical abrading is carried out by a rotary brush or the like. Next, the lithographic printing plate support is subjected to an etching treatment by an alkali agent, an electrolytic surface roughening treatment, an anodizing treatment, and the like.
In the mechanical surface roughening treatment, generally, abrading is carried out by a roller-like brush or the like while the abrasive slurry, in which an adhesive in the form of particles is suspended in water or the like, is supplied.
However, conventionally, at the time of mechanical surface roughening, the surface of the aluminum plate or the like is rubbed by the bristles of the roller-like brush, and scratches of a length of about 1 mm are formed or the abrasive pierces the surface such that a large number of indentations are formed. Further, these scratches and indentations are not removed even by the etching treatment and the electrolytic surface roughening treatment and the like carried out thereafter, and remain on the surface.
In the aforementioned mechanical abrading, recovery and reuse of the abrasive slurry are widely carried out with the intent to conserve the abrasive slurry and keep the amount of generated waste water low. However, at the time of mechanical abrading, at least a portion of the abrasive particles within the abrasive slurry are ground and become finer particles. Accordingly, when the abrasive slurry is merely recovered and reused, the finely ground abrasive particles accumulate in the abrasive slurry, and the average particle diameter of the abrasive in the abrasive slurry gradually decreases. As a result, the average particle diameter of the abrasive particles becomes excessively small, and the quality of the lithographic printing plate support is unstable.
A printing plate, which is prepared from a PS plate in which a photosensitive layer is formed on such a lithographic printing plate support, has a poor ability to withstand repeated printing. Further, when printing is carried out by using this printing plate, ink adheres to the drum of the rubber roller of the printer and ink enters into the scratches caused by the abrasive piercing the printing plate, such that there is dirtying of the non-image portions of the printed sheet surface.
In view of the aforementioned, an object of the present invention is to provide a lithographic printing plate support which becomes the support of a PS plate which has an excellent ability to withstand repeated printing and in which defects in appearance, such as blanket roller dirtying, in which the rubber drum of an offset printer is dirtied, and spot dirtying of the printed sheet surface and the like, do not occur, and to provide a method for manufacturing the lithographic printing plate support, and a PS plate having the above merits.
One aspect of the present invention is a method of manufacturing a lithographic printing plate support comprising the step of: subjecting at least one surface of a lithographic printing plate support to a mechanical surface roughening treatment by rubbing by a rotary brush while abrasive particles are supplied, the abrasive particles being such that an average particle diameter thereof is 5 to 70 xcexcm, a contained amount of particles having a particle diameter of 100 xcexcm or more is 10 wt % or less, a contained amount of particles having a particle diameter of 500 xcexcm or more is 1 wt % or less, and the contents of SiO2 is 90 wt % or more in particles.
In accordance with the above-described manufacturing method, a lithographic printing plate support is obtained which becomes the support of a PS plate having excellent ability to withstand repeated printing, and with which defects in appearance on printed sheet surfaces do not arise even if a large number of sheets are printed.
The present invention is also a method of manufacturing a lithographic printing plate support wherein a diameter of brush bristles of the rotary brush is 0.15 to 1.35 mm, and an embedding density of the brush bristles is 30 to 5000 bristles/cm2.
A PS plate, whose support is the lithographic printing plate support obtained by the above-described method of manufacturing, has the merits of having a particularly good ability to withstand repeated printing, and causing little dirtying of printed sheet surfaces.
The present invention is also a lithographic printing plate support, wherein at least one surface of the lithographic printing plate support is subjected to a mechanical surface roughening treatment by being rubbed by a rotary brush while abrasive particles are supplied, the abrasive particles being such that a particle diameter thereof is 5 to 70 xcexcm, a contained amount of particles having a particle diameter of 100 xcexcm or more is 10 wt % or less, a contained amount of particles having a particle diameter of 500 xcexcm or more is 1 wt % or less, and the contents of SiO2 is 90 wt % or more in particles.
By forming a photosensitive layer on the surface of the lithographic printing plate support which surface has been subjected to the mechanical surface roughening treatment, a PS plate can be manufactured which has an excellent ability to withstand repeated printing and with which defects in appearance on printed sheet surfaces do not arise even if a large number of sheets are printed.
The present invention is also a PS plate wherein the surface of the lithographic printing plate support, which surface has been subjected to the surface roughening treatment, is subjected to an anodizing treatment, and a photosensitive layer is formed on the surface.
This PS plate has an excellent ability to withstand repeated printing, and defects in appearance on printed sheet surfaces do not arise even if a large number of sheets are printed. Thus, the PS plate is particularly suited for offset printing for newspapers and magazines of which ability to withstand repeated printing and image quality of the printed sheet surfaces are strongly required.
Another aspect of the present invention is a lithographic printing plate support, wherein at a surface which is subjected to the surface roughening treatment and an anodizing treatment, a surface roughness Ra is from 0.3 to 1.0 xcexcm, a maximum roughness Rmax is 10 xcexcm or less, a number Pc of roughness protrusions is 15 to 35 protrusions per mm for protrusions having a protrusion height which is greater than a set value +0.3 xcexcm and a indentation depth which is deeper than the set value xe2x88x920.3 xcexcm, and a number Pc of roughness protrusions is 7 to 25 protrusions per mm for protrusions having a protrusion height which is greater than the set value +0.6 xcexcm and a indentation depth which is deeper than the set value xe2x88x920.6 xcexcm, and the number Pc of roughness protrusions is 2 to 18 protrusions per mm for protrusions having a protrusion height which is greater than the set value +1.0 xcexcm and a indentation depth which is deeper than the set value xe2x88x921.0 xcexcm.
The surface of the lithographic printing plate support is formed to be uniformly rough. Accordingly, a PS plate, which has this lithographic printing plate support as the support thereof, has the advantages of having excellent ability to withstand repeated printing, water retaining ability, tone reproducibility, difficulty of dirtying the non-image portions, and water/ink balance, as well as a small dot gain.
The present invention is also a PS plate wherein a photosensitive layer is formed on the surface of the lithographic printing plate support which surface has been subjected to a surface roughening treatment and an anodizing treatment.
Because this PS plate has excellent adhesion between the lithographic printing plate support and the photosensitive layer, the ability to withstand repeated printing is high. Further, the water retaining ability, tone reproducibility, difficulty of dirtying the non-image portions, and water/ink balance are excellent, and the dot gain is small. Moreover, defects in appearance such as blanket roller dirtying and spot dirtying and the like do not occur.
Another aspect of the present invention is a method of manufacturing a lithographic printing plate support comprising: an abrasive slurry supplying step in which an abrasive slurry is supplied to at least one surface of a lithographic printing plate support; a mechanical abrading step in which a surface of the lithographic printing plate support at a side to which the abrasive slurry has been supplied is mechanically abraded; and an abrasive slurry waste liquid recovering step in which abrasive slurry waste liquid which is generated in the mechanical abrading step is recovered, and particles, whose average particle diameter is from ⅓ to {fraction (1/10)} of an average particle diameter of abrasive particles contained in the abrasive slurry supplied in the abrasive slurry supplying step, are removed from the abrasive slurry waste liquid, and remaining slurry is returned to the abrasive slurry supplying step.
In this manufacturing method, in the abrasive slurry waste liquid recovering step, small diameter particles, which have an average particle diameter in a specific range, are removed, and the remaining slurry is used again. Thus, not only can the amount of abrasive slurry which is consumed be reduced, but also, the average particle diameter of the abrasive particles in the abrasive slurry does not become excessively large or excessively small. Accordingly, a PS plate, whose support is the lithographic printing plate support obtained by this manufacturing method, has excellent ability to withstand repeated printing. Further, when the PS plate is used in offset printing, there is little adhesion of printing ink to the blanket roller at the printer, and thus, it is difficult for so-called blanket roller dirtying to arise.
The present invention also is a method of manufacturing a lithographic printing plate support in which the average particle diameter of the abrasive in the abrasive slurry is 10 to 70 xcexcm.
A PS plate, whose support is the lithographic printing plate support obtained by this manufacturing method, has, in particular, excellent ability to withstand repeated printing and it is difficult for blanket roller dirtying to occur.
The present invention is also a method of manufacturing a lithographic printing plate support, wherein in the abrasive slurry waste liquid recovering step, the particles, whose average particle diameter is from ⅓ to {fraction (1/10)} of the average particle diameter of the abrasive particles contained in the abrasive slurry supplied in the abrasive slurry supplying step, are removed by classification by a cyclone.
A cyclone has no movable portions, and the pressure loss thereof is low as compared with that of an ordinary filter or the like. Accordingly, in this manufacturing method, little energy is required for the removal of the particles having an average particle diameter within the above range, and reliability is high.
The present invention is also a device for manufacturing a lithographic printing plate support, the device comprising: an abrasive slurry supplying device which supplies an abrasive slurry to a surface to be abraded of a lithographic printing plate support; a mechanical abrading device which mechanically abrades a surface of the lithographic printing plate support at a side to which the abrasive slurry has been supplied; and an abrasive slurry waste liquid recovering device which recovers abrasive slurry waste liquid which is generated in the mechanical abrading device, and which removes, from the abrasive slurry waste liquid, particles, whose average particle diameter is from ⅓ to {fraction (1/10)} of an average particle diameter of abrasive particles contained in the abrasive slurry supplied by the abrasive slurry supplying device, and which returns remaining slurry to the abrasive slurry supplying device. The above-described manufacturing method can be particularly suitably implemented in this manufacturing device.